Aplicação de variadores de velocidade em sistemas de climatização

Por um lado vivemos numa sociedade cujos padrões de conforto são cada vez mais exigentes, por outro encontramo-nos numa era pautada por um certo declínio económico, social e também ambiental. Não se assumindo uma estratégia que limite ou diminua essas condições de conforto resta-nos atuar de forma a que os recursos utilizados para garantir esse mesmo conforto sejam utilizados da melhor forma possível. O setor dos edifícios é responsável por uma grande parcela de consumo de energia na sociedade atual, sendo que os sistemas de climatização que dele fazem parte, apresentam.se na maioria dos casos como os grandes consumidores de energia. Nesse sentido têm sido feitos esforços enormes no sentido de encontrar soluções que garantam a eficiência energética destes sistemas. O Variador Eletrónico de Velocidade apresenta-se como uma das soluções amplamente difundidas, na vertente do controle de processos e economia de energia. A sua aplicação em sistema de climatização é mais um desses casos. Nesse sentido, numa primeira parte é feito o estudo das características e funcionamento dos Variadores de Velocidade, Sistemas de Climatização e sua aplicação conjunta. Em seguida é realizada uma aplicação informática que pretende demonstrar a economia de energia garantida por aplicação de um Variador de Velocidade.

Controlo da velocidade e posição de um tapete rolante

A utilização eficiente da energia é essencial para a competitividade económica de um país. Sendo a intensidade energética de Portugal elevada, onde a utilização de motores elétricos, absorve cerca de metade da energia elétrica consumida na indústria, a utilização de conversores eletrónicos de potência permite obter economias de energia. Nesta tese pretende-se controlar a velocidade e o posicionamento de um tapete rolante através da utilização de um conversor eletrónico de potência. Na fundamentação teórica são referidos os conceitos de variação da tensão e frequência, controle escalar e vetorial, modelação por largura de pulso (PWM) assim como a retificação e ondulação da tensão de um variador de velocidades. Na parte prática será utilizado um servo motor, controlado por um variador eletrónico de velocidades, para efetuar o referido projeto. É ainda objeto desta tese o estudo dos parâmetros fundamentais assim como a pesquisa dos parâmetros a utilizar para o desempenho pretendido.

Impacto das medidas de conservação de energia em projeto na redução da intensidade de utilização de matérias-primas na construção de um edifício

O presente trabalho pretende mostrar que a aplicação de medidas de conservação de energia (MCE) pode representar uma redução da intensidade de utilização de matérias-primas na construção de um edifício. Mais concretamente, pode representar uma redução da utilização de materiais e equipamentos, e como consequência, uma redução no esforço económico ao primeiro investimento. Podendo posteriormente representar uma redução na utilização de energia durante o período de funcionamento do edifício. A aplicação de MCE no sector da construção tem vindo a ser uma prática corrente nos novos edifícios e edifícios sujeitos a grandes intervenções de reabilitação. Esta prática deve-se à obrigatoriedade de cumprimento de requisitos regulamentares aplicados à otimização do desempenho energético dos edifícios e dos seus sistemas técnicos, nomeadamente, o RCCTE e o RSECE, entretanto revogados pelo REH e pelo RECS, respetivamente. A implementação de MCE apresenta, na maioria dos casos, benefícios económicos para o promotor do edifício, uma vez que se traduz muitas vezes, na otimização do dimensionamento dos sistemas de Aquecimento, Ventilação e Ar Condicionado (AVAC). Esta otimização permite reduzir os custos associados ao primeiro investimento, bem como na utilização de energia por parte do utilizador, logo na redução dos custos de exploração. No entanto, a falta de quantificação dos impactos do dimensionamento dos sistemas AVAC, da redução de utilização de energia e da análise do custo-benefício da sua aplicação pode condicionar o interesse na sua implementação. Neste contexto, surge a presente dissertação, por iniciativa do Instituto Soldadura e Qualidade (ISQ), aplicado a um caso prático de um edifício já construído e propriedade daquela empresa. Com este trabalho pretende-se avaliar o contributo efetivo das MCE implementadas na fase de projeto e na fase de construção, quer na otimização da dimensão de sistemas e equipamentos AVAC, por via da redução das necessidades energéticas, quer na redução de utilização de energia, permitindo, de seguida, uma avaliação custo-benefício.Na base do caso de estudo está o ECOTERMOLAB, o edifício acima referido, adquirido pelo ISQ para instalação de um laboratório de formação, investigação e desenvolvimento na área da energia. Após aquisição pelo ISQ, o edifício sofreu várias alterações/beneficiações, entre as quais a implementação de MCE, tais como, a aplicação de isolamento térmico na envolvente opaca (paredes, pavimentos e coberturas), duplicação dos vãos envidraçados simples, conferindo-lhes melhores caraterísticas térmicas, e pela aplicação de proteções solar. Foram ainda adotadas MCE aos sistemas AVAC, designadamente, pela adoção de recuperadores de calor nas Unidades de Tratamento de Ar Novo (UTAN’s) e de variadores de velocidade nas bombas de circulação de água e nos ventiladores de ar das UTAN’s. Pretendia o ISQ concluir se a aplicação de todas as MCE contribuiu de forma efetiva para o dimensionamento de sistemas e equipamentos AVAC de menor capacidade e, consequentemente, numa redução de utilização de energia. Em sequência, pretendia avaliar a viabilidade económica da aplicação de todas as MCE, estimando o sobrecusto inicial e o tempo necessário para o retorno financeiro daquele investimento. Para alcançar os objetivos propostos, procedeu-se à simulação energética dinâmica do ECOTERMOLAB, utilizando o programa EnergyPlus. Primeiro foi simulada uma situação base do edifício, sem quaisquer MCE. Posteriormente foi caraterizada cada uma das situações de aplicação das MCE, com o objetivo de avaliar o respetivo impacto individual na utilização de energia pelos sistemas AVAC. Por último foram assumidas todas as soluções em conjunto para avaliar o impacto final de todas as MCE na utilização de energia dos sistemas AVAC, bem como no seu dimensionamento. Das simulações dinâmicas foram obtidos os valores das necessidades de aquecimento e arrefecimento, de energia utilizada pelos sistemas AVAC e de caudais de água aquecida e arrefecida circulada. Com estes valores foi feita uma estimativa de dimensionamento dos equipamentos e componentes AVAC para as situações da aplicação de todas as MCE no ECOTERMOLAB e a sua ausência. A partir da diferença dos custos de aquisição dos respetivos equipamentos e dos valores de poupança em energia foi realizado o estudo da viabilidade económica da implementação das MCE neste edifício. Este estudo permitiu concluir que a aplicação das MCE no ECOTERMOLAB levou à redução da dimensão na generalidade dos equipamentos e componentes AVAC. Permitiu, ainda, concluir que houve uma diminuição de utilização de energia por parte destes sistemas e equipamentos para o aquecimento e arrefecimento. Conclui-se ainda que o período de retorno (Payback) do sobrecusto inicial, estimado em 37.822€ é de, aproximadamente, onze anos e meio, para um valor atual líquido (VAL) de 8.061€ e à taxa interna de rentabilidade (TIR) de 7,03%.

Aktiivisten magneettilaakereiden tilasäädön mallinnus ja simulointi

Aktiivisten magneettilaakereiden avulla on mahdollista kannatella ferromagneettisia kappaleita, kuten sähkökoneiden roottoreita, ilman fyysistä kontaktia. Magneettilaakerit tarjoavat monia etuja, kuten esimerkiksi kitkattomuuden, verrattuina perinteisiin mekaanisiin laakereihin. Nämä edut vielä korostuvat suurnopeuskäytöissä, jotka ovat magneettilaakereiden pääasiallisia käyttökohteita. Tässä työssä esitellään magneettilaakereihin liittyvät erusteoriat ja niiden sovellustavat. Tämän jälkeen tarkastellaanmagneettilaakereiden kanssa käytettäviä säätöratkaisuja ja esitetään niille soveltuvat viritysmenetelmät. Teorioiden pohjalta rakennetaan täydellinen magneettilaakerijärjestelmän simulointimalli säätöratkaisuineen ja suoritetaan järjestelmän toimintaa kuvaavia simulointeja. Simuloinneissa saadut tulokset pyritään vielä varmentamaan suorittamalla mittauksia koelaitteistolla ja vertaamalla saatuja tuloksia keskenään.

DTC-induktiomoottorikäytön soveltaminen keskitaajuusalueelle

Työssä tarkastellaan olemassa olevan suoraa vääntömomentin säätöä käyttävän taajuudenmuuttajan soveltamista keskitaajuusalueella toimiviin induktiomoottorikäyttöihin. Keskinopeusalueen sovellusten pyörimisnopeudet ovat tyypillisesti 6000…30000rpm. Tällöin invertterin lähtötaajuuden on nelinapaista moottoria ohjattaessa ulotuttava 1000Hz:iin. ABB:n ACS600 taajuudenmuuttajan nykyinen syöttötaajuus ulottuu noin 400Hz:iin ja sen keskimääräinen kytkentätaajuus on luokkaa 3kHz. Taajuudenmuuttajan keskimääräistä kytkentätaajuutta ei haluta tästä merkittävästi nostaa, koska tällöin pääteasteen mitoitusta ja rakennetta on muutettava. Tarkastelussa keskitytään täten jännitemodulointiin, joka määrittelee invertterin lähtöjännitteen käyrämuodon ja pääteasteen tehokytkimien kytkentätaajuuden. Työssä esitetään suoran käämivuon säädön periaatetta soveltava 30-kulmainen modulointimenetelmä (30-modulointi), jolla moottorin syöttövirrasta voidaan eliminoida 5. ja 7. yliharmoninen komponentti. Yliharmonisten komponenttien eliminointi mahdollistaa passiivisilla komponenteilla toteutetun alipäästösuodattimen asentamisen invertterin lähtöön, jolloin moottorissa tapahtuvat tehohäviöt saadaan pieniksi. 30-moduloinnin ohjaukseen ja säätöön esitetään menetelmät, jotka mahdollistavat sen toteuttamisen nykyiseen taajuudenmuuttajaan ohjelmallisesti ilman suuria laitteistomuutoksia. 30-moduloinnin ominaisuuksia tarkastellaan analyyttisin menetelmin ja sen toimintaa testataan esitettyjen teorioiden perusteella simuloimalla. 30-moduloinnin ohjelmallinen implementointi nykyiseen ACS600:een mahdollistaa periaatteessa noin 600Hz:n syöttötaajuuden saavuttamisen. Tällöin invertterin keskimääräinen kytkentätaajuus voidaan säätää koko pyörimisnopeusalueella alle 4kHz:n tasolle.

Supplier Energy Audits in Thermal Power Plants

This master’s thesis handles an operating model for an electric equipment supplier conducted sale oriented energy audit for pumping, fan and other motor applications at power plants. The study goes through the largest factors affecting internal electricity use at a power plant, finds an energy audit –like approach for the basis of information gathering and presents the information needed for conducting the analysis. The model is tested in practice at a kraft recovery boiler of a chemical pulping mill. Targets chosen represent some of the largest electric motor applications in the boiler itself and in its fuel handling. The energy saving potential of the chosen targets is calculated by simulating the energy consumption of the alternatives for controlling the targets, and thereafter combining the information with the volume flow duration curve. Results of the research are somewhat divaricated, as all the information needed is not available in the automation system. Some of the targets could be simulated and their energy saving potential calculated quite easily. At some of the targets chosen the monitoring was not sufficient enough for this and additional measurements would have been needed to base the calculations on. In traditional energy audits, energy efficiency of pump and fan applications is not necessarily examined. This means that there are good possibilities for developing the now presented targeted energy audit procedure basis further.

Comparison of Model-Based Flow Rate Estimation Methods in Frequency-Converter-Driven Pumps and Fans

Fluid handling systems such as pump and fan systems are found to have a significant potential for energy efficiency improvements. To deliver the energy saving potential, there is a need for easily implementable methods to monitor the system output. This is because information is needed to identify inefficient operation of the fluid handling system and to control the output of the pumping system according to process needs. Model-based pump or fan monitoring methods implemented in variable speed drives have proven to be able to give information on the system output without additional metering; however, the current model-based methods may not be usable or sufficiently accurate in the whole operation range of the fluid handling device. To apply model-based system monitoring in a wider selection of systems and to improve the accuracy of the monitoring, this paper proposes a new method for pump and fan output monitoring with variable-speed drives. The method uses a combination of already known operating point estimation methods. Laboratory measurements are used to verify the benefits and applicability of the improved estimation method, and the new method is compared with five previously introduced model-based estimation methods. According to the laboratory measurements, the new estimation method is the most accurate and reliable of the model-based estimation methods.

Energy Analysis within Industrial Hydraulics and Correspondent Solar PV System Design

Energy efficiency and renewable energy use are two main priorities leading to industrial sustainability nowadays according to European Steel Technology Platform (ESTP). Modernization efforts can be done by industries to improve energy consumptions of the production lines. These days, steel making industrial applications are energy and emission intensive. It was estimated that over the past years, energy consumption and corresponding CO2 generation has increased steadily reaching approximately 338.15 parts per million in august 2010 [1]. These kinds of facts and statistics have introduced a lot of room for improvement in energy efficiency for industrial applications through modernization and use of renewable energy sources such as solar Photovoltaic Systems (PV).The purpose of this thesis work is to make a preliminary design and simulation of the solar photovoltaic system which would attempt to cover the energy demand of the initial part of the pickling line hydraulic system at the SSAB steel plant. For this purpose, the energy consumptions of this hydraulic system would be studied and evaluated and a general analysis of the hydraulic and control components performance would be done which would yield a proper set of guidelines contributing towards future energy savings. The results of the energy efficiency analysis showed that the initial part of the pickling line hydraulic system worked with a low efficiency of 3.3%. Results of general analysis showed that hydraulic accumulators of 650 liter size should be used by the initial part pickling line system in combination with a one pump delivery of 100 l/min. Based on this, one PV system can deliver energy to an AC motor-pump set covering 17.6% of total energy and another PV system can supply a DC hydraulic pump substituting 26.7% of the demand. The first system used 290 m2 area of the roof and was sized as 40 kWp, the second used 109 m2 and was sized as 15.2 kWp. It was concluded that the reason for the low efficiency was the oversized design of the system. Incremental modernization efforts could help to improve the hydraulic system energy efficiency and make the design of the solar photovoltaic system realistically possible. Two types of PV systems where analyzed in the thesis work. A method was found calculating the load simulation sequence based on the energy efficiency studies to help in the PV system simulations. Hydraulic accumulators integrated into the pickling line worked as energy storage when being charged by the PV system as well.

DCM Boost interleaved converter for operation in AC and DC to trolleybus application

This paper is based on the development and experimental analysis of a DCM Boost interleaved converter suitable for application in traction systems of electrical vehicles pulled by electrical motors (Trolleybus), which are powered by urban DC or AC distribution networks. This front-end structure is capable of providing significant improvements in trolleybuses systems and in the urban distribution network costs, and efficiency. The architecture of proposed converter is composed by five boost power cells in interleaving connection, operating in discontinuous conduction mode. Furthermore, the converter can operate as AC-DC converter, or as DC-DC converter providing the proper DC output voltage range required by DC or AC adjustable speed drivers. Therefore, when supplied by single-phase AC distribution networks, and operating as AC-DC converter, it is capable to provide high power factor, reduced harmonic distortion in the input current, complying with the restrictions imposed by the IEC 61000-3-4 standards. The digital controller has been implemented using a low cost FPGA and developed totally using a hardware description language VHDL and fixed point arithmetic. Thus, two control strategies are evaluated considering the compliance with input current restrictions imposed by IEC 61000-3-4 standards, the regular PWM modulation and a current correction PWM modulation. In order to verify the feasibility and performance of the proposed system, experimental results from a 15 kW low power scale prototype are presented, operating in DC and AC conditions.

A simplified method for determining the high frequency induction motor equivalent electrical circuit parameters to be used in EMI effect

The aim of this paper is to present a simple method for determining the high frequency parameters of a three-phase induction motor to be used in studies involving variable speed drives with PWM three-phase inverters, in which it is necessary to check the effects caused to the motor by the electromagnetic interference, (EMI) in the differential mode, as well as in the common mode. The motor parameters determination is generally performed in adequate laboratories using accurate instruments, such as very expensive RLC bridges. The method proposed here consists in the identification of the motor equivalent electrical circuit parameters in rated frequency and in high frequency through characteristic tests in the laboratory, together with the use of characteristic equations and curves, shown in the references to be mentioned for determining the motor high frequency parasite capacitances and also through system simulations using dedicated software, like Pspice, determining the characteristic waveforms involved in the differential and common mode phenomena, comparing and validating the procedure through published papers [01].

Análise de viabilidade técnica-econômica para a aplicação de inversores de frequência em sistemas de bombeamento de baixa potência

Pós-graduação em Engenharia Mecânica - FEG

Retificador entrelaçado com elevado fator de potência para operação de um veículo trólebus alimentado por redes em CA Ou CC

This paper presents the development and the main results for an interleaved boost rectifier operating as a special input power stage for a trolleybus type vehicle, allowing its feeding by alternate current (AC) or direct current (DC) distribution power systems. When feeding with two wires (single phase) alternate current distribution system, the converter accomplish active power factor correction, providing a relatively sinusoidal current with low total harmonic distortion (THD) and fully complying with IEC 61000-3-4 standards. In addition, a management control system promotes the required automatic operation changes for the proposed rectifier when the vehicle is changing from the DC distribution power system to the AC distribution power system and vice-versa, keeping its original electrical DC system characteristics for the adjustable speed driver sub-system. The main experimental results for a prototype rated at 150kW are presented, considering its application for a trolleybus with DC adjustable speed driver, demonstrating the proposed converter benefits and the possibility of AC feeding system for trolleybus type vehicle.

Novel simulation methods for Coulomb and hydrodynamic interactions

This thesis presents new methods to simulate systems with hydrodynamic and electrostatic interactions. Part 1 is devoted to computer simulations of Brownian particles with hydrodynamic interactions. The main influence of the solvent on the dynamics of Brownian particles is that it mediates hydrodynamic interactions. In the method, this is simulated by numerical solution of the Navier--Stokes equation on a lattice. To this end, the Lattice--Boltzmann method is used, namely its D3Q19 version. This model is capable to simulate compressible flow. It gives us the advantage to treat dense systems, in particular away from thermal equilibrium. The Lattice--Boltzmann equation is coupled to the particles via a friction force. In addition to this force, acting on {it point} particles, we construct another coupling force, which comes from the pressure tensor. The coupling is purely local, i.~e. the algorithm scales linearly with the total number of particles. In order to be able to map the physical properties of the Lattice--Boltzmann fluid onto a Molecular Dynamics (MD) fluid, the case of an almost incompressible flow is considered. The Fluctuation--Dissipation theorem for the hybrid coupling is analyzed, and a geometric interpretation of the friction coefficient in terms of a Stokes radius is given. Part 2 is devoted to the simulation of charged particles. We present a novel method for obtaining Coulomb interactions as the potential of mean force between charges which are dynamically coupled to a local electromagnetic field. This algorithm scales linearly, too. We focus on the Molecular Dynamics version of the method and show that it is intimately related to the Car--Parrinello approach, while being equivalent to solving Maxwell's equations with freely adjustable speed of light. The Lagrangian formulation of the coupled particles--fields system is derived. The quasi--Hamiltonian dynamics of the system is studied in great detail. For implementation on the computer, the equations of motion are discretized with respect to both space and time. The discretization of the electromagnetic fields on a lattice, as well as the interpolation of the particle charges on the lattice is given. The algorithm is as local as possible: Only nearest neighbors sites of the lattice are interacting with a charged particle. Unphysical self--energies arise as a result of the lattice interpolation of charges, and are corrected by a subtraction scheme based on the exact lattice Green's function. The method allows easy parallelization using standard domain decomposition. Some benchmarking results of the algorithm are presented and discussed.

Development of physics-based models and design optimization of power electronic conversion systems

The main objective for physics based modeling of the power converter components is to design the whole converter with respect to physical and operational constraints. Therefore, all the elements and components of the energy conversion system are modeled numerically and combined together to achieve the whole system behavioral model. Previously proposed high frequency (HF) models of power converters are based on circuit models that are only related to the parasitic inner parameters of the power devices and the connections between the components. This dissertation aims to obtain appropriate physics-based models for power conversion systems, which not only can represent the steady state behavior of the components, but also can predict their high frequency characteristics. The developed physics-based model would represent the physical device with a high level of accuracy in predicting its operating condition. The proposed physics-based model enables us to accurately develop components such as; effective EMI filters, switching algorithms and circuit topologies [7]. One of the applications of the developed modeling technique is design of new sets of topologies for high-frequency, high efficiency converters for variable speed drives. The main advantage of the modeling method, presented in this dissertation, is the practical design of an inverter for high power applications with the ability to overcome the blocking voltage limitations of available power semiconductor devices. Another advantage is selection of the best matching topology with inherent reduction of switching losses which can be utilized to improve the overall efficiency. The physics-based modeling approach, in this dissertation, makes it possible to design any power electronic conversion system to meet electromagnetic standards and design constraints. This includes physical characteristics such as; decreasing the size and weight of the package, optimized interactions with the neighboring components and higher power density. In addition, the electromagnetic behaviors and signatures can be evaluated including the study of conducted and radiated EMI interactions in addition to the design of attenuation measures and enclosures.

Projeto iterativo, simulação, análise e otimização de máquina a relutância variável monofásica

Variable reluctance motors have been increasingly used as an alternative for variable speed and high speed drives in many industrial applications, due to many advantages like the simplicity of construction, robustness, and low cost. The most common applications in recent years are related to aeronautics, electric and hybrid vehicles and wind power generation. This paper explores the theory, operation, design procedures and analysis of a variable reluctance machine. An iterative design methodology is introduced and used to design a 1.25 kW prototype. For the analysis of the machine two methods are used, an analytical method and the finite element simulation. The results obtained by both methods are compared. The results of finite element simulation are used to determine the inductance profiles and torque of the prototype. The magnetic saturation is examined visually and numerically in four critical points of the machine. The data collected in the simulation allow the verification of design and operating limits for the prototype. Moreover, the behavior of the output quantities is analyzed (inductance, torque and magnetic saturation) by variation of physical dimensions of the motor. Finally, a multiobjective optimization using Differential Evolution algorithms and Genetic Algorithms for switched reluctance machine design is proposed. The optimized variables are rotor and stator polar arcs, and the goals are to maximize the average torque, the average torque per copper losses and the average torque per core volume. Finally, the initial design and optimized design are compared.